Diesel fuel combustion systems raise many challenges for emissions control. Conventional strategies for reducing particulate, hydrocarbon, and nitrogen oxide (NOx) emissions include optimizing fuel injection and air motion, effective fuel atomization at varying loads, control of time of fuel injection, minimization of parasitic losses in combustion chambers, low sac volume or valve cover orifice nozzles for direct injection, reducing lubrication oil contributions, and rapid engine warm up.
Diesel particulate traps such as catalyzed diesel particulate filters (C-DPFs) and continuously regenerating technology diesel particulate filters (CRT-DPFs) have been developed which employ ceramic or metal filters. Thermal and catalytic regeneration can burn out the trapped material. New particulate standards may necessitate such traps. Fuel composition, including sulfur and aromatic content, and the burning of lubricant can contribute to increased particulate emissions. Catalysts have been developed for diesel fuels which are very effective in oxidizing the organic portion of the particulate.
It is also recognized that dispersions of water in diesel fuel may serve to reduce undesirable diesel emissions such as carbon monoxide, particulates and NOx. See, e.g., U.S. Pat. Nos. 5,669,938; 5,404,841; 5,535,708; 5,584,894; 5,809,774. Notwithstanding all of the foregoing teachings, particulate matter still builds up in diesel particulate filters. This build up, over time, creates backpressure on the combustion system, thereby decreasing the efficiency and power of the system. Additionally, the build up of particulate within a particulate filter system also reduces the efficiency of that system as an emissions control device. The built up particulate may block surfaces within the filter that may otherwise catalyze the break down of undesirable emissions by-products.
U.S. Patent Application 2003/0196430 A1 teaches a process for reducing the level of pollutants in the exhaust of a diesel engine.